Environment deterioration and related fungal infection of Upper Jurassic horseshoe crabs with remarks on their exceptional preservation

Approximately 10% of Late Jurassic (Tithonian) horseshoe crabs collected from the Kcynia Formation in the Owadów-Brzezinki Quarry, Central Poland, display microborings covering the entire carapace of specimens. Detailed examination of the surrounding sediment indicates the occurrence of short-term fluctuations in the oxygenation level of bottom waters and their salinities. The identified palynomorph assemblage from the sediment suggests pathogenic algal blooms as the probable cause for mass mortality. Anoxic conditions resulting from algal blooms in restricted environments facilitated fungal infection evidenced by the damage (microborings) caused by the hyphae on the surface of the exoskeletons. Associated biochemical factors contributed to the excellent preservation of diversified fauna with soft tissues.